1. Field of the Invention
The present invention relates in general to a lock system for a back door of a motor vehicle, and more particularly to a lock system for a back door of a type having an auxiliary door pivotally mounted thereto. More specifically, the present invention is concerned with a lock system which can selectively operate a first lock device of a main door and a second lock device of an auxiliary door hinged to the main door.
2. Description of the Prior Art
In order to clarify the task of the present invention, a conventional lock system of the above-mentioned type will be outlined with reference to FIG. 21, which is disclosed in Japanese Patent First Provisional Publication No. 57-191125.
Referring to FIG. 21, a so-called "hinged window-mounted door" a is shown as a back door of a delivery van type motor vehicle. The back door a comprises a main door part c hinged at its upper end to a vehicle body b to open and close a back opening of the vehicle, and an auxiliary door part e hinged to the main door part c to open and close a window opening d formed in the same.
In order to releasably hold the main door part c and the auxiliary door part e in their closed positions, first and second lock devices f and g are independently mounted to the back door. Upon request of opening the main door part c, the first lock device f is manipulated to release the main door part c, while, upon request of opening the auxiliary door part e, the second lock device g is manipulated to release the auxiliary door part. That is, in the conventional door lock system, opening operations of the main and auxiliary door parts c and e are independently carried out by respective lock devices f and g.
However, due to this inherent construction, the above-mentioned conventional lock system may induce the following undesirable matters. That is, if, with a baggage h carried on the roof of the vehicle, the main door part c is brought into open position with the auxiliary door part e opened, it may occur that the auxiliary door part e collides against an edge of the baggage h resulting in brekage of the same. The problems of this type are frequently and unavoidably carried out by absentminded persons.
Of course, these problems may be solved when the maximum open angles of the main and auxiliary door parts c and e are restrained to small degrees. However, in this case, loading and unloading of goods through the back door opening of the vehicle become difficult and at least troublesome.
Furthermore, since the conventional lock system has two key cylinder devices for the respective lock devices, a person unfamiliar with the vehicle may be confused in finding a proper key cylinder for opening a desired door part.